The present invention relates to a method and device for controlling an automatic transmission, and particularly relates to a method and device for controlling an automatic transmission mounted on a vehicle.
Automatic transmissions mounted on vehicles, such as automobiles, include a torque converter and a transmission gear mechanism, and automatically perform a gear shift operation by suitably setting operating states of a plurality of frictional engageable elements, such as clutches and brakes (i.e., by selecting a suitable drive force transmitting path), according to a driving condition of the vehicle.
The gear control of such an automatic transmission is required to shorten the time for completing the engagement after a gear shift command is issued and reduce an engaging shock as much as possible when switching the operating states of the frictional engageable elements from disengaged states to engaged states. For example, WO2012/144207A1 discloses a method for executing a pre-charging process when supplying hydraulic pressure to a frictional engageable element to engage the frictional engageable element. This pre-charging process quickly charges hydraulic oil in an oil path leading to the frictional engageable element from a hydraulic pressure control valve that controls the oil supply, and in a hydraulic pressure chamber of the frictional engageable element.
The pre-charging process is executed by a sharp increase of hydraulic pressure to a given value in response to the gear shift command, maintaining of the increased pressure for a given period of time, and a sharp drop of the hydraulic pressure to a given pressure thereafter.
The method of WO2012/144207A1 requires flowing hydraulic oil at a high flow rate (e.g., at the pre-charged hydraulic pressure) in order to shorten the time of the engagement control, while reducing the flow rate of the hydraulic oil (drop the hydraulic pressure) immediately before the completion of one stroke of a piston in order to reduce an engaging shock. In this case, a fine flow rate control is required and a hydraulic pressure control tends to become complex. Therefore, inconveniences of the engagement control being time consuming and responses of the frictional engageable elements becoming slower, arise. The slower responses of the frictional engageable elements become significantly inconvenient when attempting to further shorten the gear shifting time.
The control employing the pre-charging in the engaging operation also requires constant learning of the pre-charging time and feedbacks. For this reason, the control may become complex.
Further, the state of the automatic transmission changes with time, for example, a temperature of the hydraulic oil changes due to operation and a viscosity of the hydraulic oil changes due to aging. Even after the state of the automatic transmission changed, the automatic transmission is requested to shorten an engagement control time in a gear shift operation and reduce an undesirable engaging shock that a vehicle driver did not expect.